1. Field of the Invention
The invention relates to a device for separating liquid and/or gas components from each other, which device includes a ceramic membrane comprising a porous layer of xcex3-alumina which is present on top of a porous layer of supporting material, that is, the carrier, and also to the membrane used in such a device.
2. Description of the Related Art
The separation of different molecules which are present in liquids or gases is frequently an important part of industrial chemical processes. Industrial separating techniques are traditionally based on distillation, crystallisation, absorption, extractions and/or cryogenic techniques. One drawback of said techniques is the fact that they require a great deal of energy as well as significant investment.
Consequently, there is a need for separation techniques which require less energy and which can be used both on a large scale and on a small scale. In this connection, membranes are frequently used for separating or filtrating gases of liquids at a molecular level. There are various kinds of membranes, among which polymeric and ceramic membranes. Ceramic membranes are finding increasingly wide industrial application.
Some advantages of ceramic membranes in comparison with polymeric membranes are their greater thermal and chemical stability, mechanical strength, selectivity and through-flow rate.
A number of specific applications are steam sterilisation for the foodstuffs industry and the medical industry, filtration of steam containing hot waste gases in the process industry, and membrane reactors, such as steam reformers and dehydrogenation reactors.
For ultrafiltration purposes, the filter layer frequently consists of xcex3-alumina, a mesoporous material, which may be applied on top of a layer of macroporous xcex1-alumina. For gas filtration purposes, a silica layer, a microporous material, may furthermore be applied to the xcex3-alumina layer. In that case the xcex3-alumina layer functions as a bridging layer between the large pores of the carrier and the very small pores of the silica layer.
One drawback of the use of this kind of ceramic membranes in the aforesaid industrial processes is their limited resistance to certain substances, such as steam, whereby the xcex3-alumina layer may come loose under the influence of the steam of the carrier. Said coming loose of the xcex3- alumina layer may also lead to the fracture of the silica layer that may be present, as a result of which the function of such a membrane will be lost.
The object of the invention is to provide a membrane having a long life, which provides a stable bond between the xcex3-alumina layer and the carrier.
In order to accomplish that objective, an alkali-free, phosphorous material is present between said supporting material and said layer of xcex3-alumina. In practice it has become apparent that such a phosphorous material is conducive towards obtaining a good bond between the two layers, which bond appears to be properly resistant to, inter alia, steam.
Preferably, said alkali-free, phosphorous material substantially consists of monoaluminium phosphate, and said supporting material consists substantially of alumina and/or titania and/or zirconia and/or silica and/or metal compounds. Such materials, which are known per se, appear to be satisfactory in practice for obtaining a stable and reliable membrane.
In one preferred embodiment, a porous top layer having smaller pores, preferably a top layer which contains silica, is present on top of said porous layers of xcex3-alumina, as a result of which a satisfactory gas separation filter is obtained.
The invention furthermore relates to a method for separating liquid and/or gas components from each other, wherein said liquid and/or said gas is passed through a ceramic membrane comprising a porous layer of xcex3-alumina which is present on a porous layer of supporting material, wherein an alkali-free, phosphorous material is present between said supporting material and said layer of xcex3-alumina.
The invention furthermore relates to a method for manufacturing a ceramic membrane for separating liquid and/or gas components from each other, wherein a porous layer of xcex3-alumina is applied to a porous layer of supporting material, characterized in that an alkali-free, phosphorous material is provided between said supporting material and said layer of xcex3-alumina. In one preferred embodiment, an aqueous solution of monoaluminium phosphate is applied to said supporting material, after which the membrane is slowly heated and maintained at a temperature of more than 250 degrees Celsius for at least two hours, followed by slow cooling, after which the layer of xcex3-alumina is applied. In this manner a stable bond is obtained.